1. Field of Invention
The present invention relates to a projection display device for projecting in enlarged form an image through a projection optical system as a result of separating a plurality of color light beams from a light source, modulating the color light beams by light-modulating elements in accordance with image information, and synthesizing the modulated color light beams.
2. Description of Related Art
A conventional projection display device primarily comprises a light source unit, an optical unit for optically treating the light from the light source unit so as to synthesize color images in accordance with image information, and a projecting lens for projecting in enlarged form an image, formed by synthesizing the light beams, onto a screen.
FIG. 13(A) is a schematic structural view of the conventional optical unit and projecting lens. As shown in this figure, the optical unit 3 comprises a light source 20; a color separation optical system 40 for separating a light beam W, emitted from the light source 20, into the three primary light beams, namely, the red light beams (R), the green light beams (G), and the blue light beams (B); three liquid crystal panels (light-modulating elements) 5R, 5G, and 5B, for modulating each of the different color light beams in accordance with image information; a cross dichroic prism 60 for synthesizing each of the modulated color light beams; and a projecting lens 4 for projecting in enlarged form an image, formed by synthesizing the different color light beams, onto a screen 120. The light beam W, emitted from the light source 20, is separated into the color light beams, R, G, and B, by the color separation optical system 40 comprising various dichroic mirrors. Of the color light beams, the red light beams R and the green light beams G are emitted towards corresponding liquid crystal panels 5R and 5G from their corresponding light emitting portions in the color separation optical system 40. The blue light beams B are guided towards the liquid crystal panel 5B via a light-guiding optical system 50.
In the optical unit 3 illustrated in enlarged form in FIGS. 13(B) and 13(C), polarizing plates 100R, 100G, and 100B are disposed at the light-incoming surface side of corresponding liquid crystal panels 5R, 5G, and 5B. The polarizing plates 100R, 100G, and 100B are provided to align the polarization planes of the different color light beams incident upon the corresponding liquid crystal panels 5R, 5G, and 5B. Polarizing plates 110R, 110G, and 110B are disposed at the light emitting side of the corresponding liquid crystal panels 5R, 5G, and 5B. The polarizing plates 110R, 110G, and 110B are provided to align the polarization planes of the different modulated color light beams that are going to strike the cross dichroic prism 60. The polarizing plates allows an image with high contrast to be projected onto the screen 120. Of the polarizing plates sandwiching their corresponding liquid crystal panels 5R, 5G, and 5B, the polarizing plates 110R, 110G, and 110B are adhered to the light emitting surface of their corresponding liquid crystal panels.
A generally used polarizing plate comprises a polarizer and a protective layer laminated thereto, with the polarizer formed of a dichroic material such as an iodine-containing material or organic dye. For the liquid crystal panels, an active matrix type liquid crystal device is generally used, in which type of liquid crystal device the pixels disposed in a matrix arrangement are controlled by a switching element.
Here, an effective way of increasing contrast of the image projected in enlarged form onto the screen 120 is to adhere a polarizing plate with good polarization selection characteristics to the light emitting surface of each of the liquid crystal panels 5R, 5G, and 5B. However, polarizing plates with excellent selection characteristics correspondingly absorb a larger amount of light, so that a large amount of heat is generated thereat. The above-described projection display device is constructed so that the polarizing plates are cooled by air currents formed in the projection display device, as shown in FIG. 13(C). However, since the polarizing plates are directly adhered to the light emitting surface of their respective liquid crystal panels, the polarizing plates transmit heat to the liquid crystal panels easily, so that the temperature of the liquid crystal panels tends to rise. This temperature rise deteriorates optical characteristics of the liquid crystal panels, reducing contrast of the projected image.
Heat transfer to the liquid crystal panels may be kept low by disposing the polarizing plates so that they are separated from the light emitting surface of their respective liquid crystal panels. However, when the polarizing plates are merely separated from their respective light emitting surfaces, dust or the like sticks onto the light emitting surface of the liquid crystal panels by the air currents flowing in the display, causing a reduction in the quality of the projected image.
In view of the above-described problems, it is one aspect of the present invention to provide a projection display device which can prevent deterioration in the optical characteristics of the light-modulating elements caused by heat generated at the polarizing plates. In addition, it is an object of the present invention to provide a projection display device which can project a high quality image unaffected by dust or the like, even when it gets scattered by air currents in the projection display device.
To overcome the above-described problems, according to the present invention, there is provided a projection display device including a color separator for separating light emitted from a light source into a plurality of color light beams; a plurality of light-modulating elements for modulating the plurality of color light beams, formed as a result of separation by the color separator, in accordance with image information; a color synthesizer for synthesizing the color light beams modulated by the respective light-modulating elements; and a projector for projecting in enlarged form an image formed by the resulting light beam formed by the color synthesizer. In addition, at least one of the plurality of color light beams may be a blue light beam, and a light transmissive plate may be disposed at at least one of the light-incoming surface and the light emitting surface of the light-modulating elements modulating the color light beams other than the blue light.
According to the projection display device of the present invention, a light transmissive plate may be provided at the light-incoming surface, or the like, of the corresponding light-modulating elements other than that for blue light. In this case, the light transmissive plate or plates are disposed between the corresponding light-modulating elements and the corresponding polarizing plate or plates, and reduces the amount of heat transmission from polarizing plate or plates to the corresponding light-modulating elements. Therefore, rises in temperature of the polarizing plate due to the heat generated at the polarizing plate or plates, can be reduced, making it possible to obviate the problem of deterioration in the optical characteristics of the light-modulating elements. In addition, since the light-incoming surface, or the like, of the light-modulating elements are protected by the corresponding light transmissive plate or plates, it is possible to prevent direct sticking of dust, or the like, onto the light-incoming surface or surfaces even when, for example, dust is scattered by air currents in the projection display device. Consequently, dust does not appear on the projection surface.
Here, since the energy per unit quantity of light for short wavelengths of light is higher than for long wavelengths of light, the amount of heat generated at a polarizing plate disposed at the light-incoming surface side or at the light emitting surface side of the light-modulating element for blue light is very large compared to that generated at the polarizing plate or plates disposed near the other light-modulating elements. Therefore, when a light transmissive plate is provided at the light-modulating element for blue light, it is hard to sufficiently reduce the heat transmission from the polarizing plate or plates to the light-modulating element by the light transmissive plate, because of the larger amount of generated heat. Consequently, in this case, the light transmissive plate acts to prevent heat dissipation at the light-modulating element, making it easier for the temperature of the light-modulating element to rise.
According to the projection display device of the present invention, a light transmissive plate may be provided at the light-modulating elements other than that for blue light, so the heat can be efficiently dissipated at the light-modulating element for blue light, thereby reducing the amount rise in temperature of the light-modulating elements for blue light. Therefore, it is possible to prevent deterioration in the optical characteristics of the light-modulating element for blue light. It is to be noted that since a light transmissive plate is not provided at the light-modulating element for blue light, the light-incoming and the light emitting surfaces of the light-modulating element are exposed, so that dust or the like may directly stick onto these surfaces. However, the relative luminosity factor for blue light is low compared to that of other colors, so that even when dust sticks onto the light-incoming and the light emitting surfaces, the dust does not easily show on the projection surface, thus making it possible to prevent the quality of the projected image from being reduced.
Accordingly, it is possible to prevent deterioration in the optical characteristics, caused by a temperature rise, of all of the light-modulating elements. In addition, even when dust or the like is scattered by air currents in the projection display device, the image is not affected by it, so that a high quality image can be projected.
According to the projection display device of the present invention, a dust protection member may be provided to cover the area between a light transmissive plate and, for example, the light-incoming surface of a light-modulating element, instead that the light transmissive plate is provided at, for example, the light-incoming surface of the light-modulating element.
In this structure, since the area between the light-modulating elements, other than that for blue light, and the polarizing plate or plates are covered by the dust protection member or members, an air layer is formed between the light-modulating elements and light transmissive plate or plates. Consequently, the air layer and light transmissive plate or plates is provided between the polarizing plate or plates and the corresponding light-modulating elements. Accordingly, the air layer or layers and the light transmissive plate or plates reduce the heat transmission from the polarizing plate or plates and transmitted to the light-modulating elements, making it possible to reduce the amount of rise in temperature of the light-modulating elements due to heat generated at the polarizing plate or plates. This can obviate the problem of deterioration in the optical characteristics of the light-modulating elements. In addition, since the air layer or layers are covered by the dust protection member or members, it is possible to prevent dust or the like from entering the air layer or layers. Therefore, dirt can be prevented from sticking onto the light emitting surface of the light-modulating elements.
On the other hand, since a light transmissive plate and a dust protection member are not disposed at the light-modulating element for blue light, the problem that the light transmissive plate and the dust protection member interfere with heat dissipation at the light-modulating element does not occur, thereby allowing efficient cooling of the light-modulating element. Thus, it is possible to prevent the temperature of the light-modulating element for blue light from rising, and thus also preventing the deterioration in the optical characteristics thereof. In addition, since the relative luminosity factor for blue light is low, the quality of the projected image is not reduced even when a light transmissive plate or a dust protection member is not provided.
Therefore, even in this structure, it is possible to prevent deterioration in the optical characteristics, caused by a temperature rise, of all of the light-modulating elements. In addition, even when dust or the like is scattered in the projection display device by air currents, the image is not affected by it, so that a high quality image can be projected.
Here, not only can the polarizing plate be of the commonly used type which transmits one type of polarized light and absorbs the other type of polarized light. It can also be a reflection type polarizing plate which reflects the other type of polarized light. The reflection type polarizing plate absorbs only a small amount of light, and thus generates only a small amount of heat. Therefore, the usage of the reflection type polarizing plate can further reduce the amount of rise in temperature. However, when a reflection type polarizing plate is disposed at the light emitting surface side of a light-modulating element, the light reflected by the polarizing plate may irradiate the light-modulating element and cause it to malfunction. Therefore, it is desirable that the polarizing plate disposed at the light-incoming surface side of a light-modulating element be a reflection type polarizing plate.
The projection display device of the present invention may be of the type which separates light from a light source into a plurality of different color light beams, such as three different color light beams, red light beams, green light beams, and blue light beams.
Here, it is desirable that the dust protection member support its associated light-modulating element and its associated light transmissive plate, and be removably secured to the light-incoming surface of the color synthesizer. In this case, it is not necessary to directly touch the light-modulating elements in order to mount them at the side of the color synthesizer, so that it is possible to eliminate the problem of breakage or defects in the light-modulating elements occurring when they interfere with other component parts. In addition, it is easier to replace light-modulating elements.